Silicon carbide (SiC) substrates are known for their use in semiconductor manufacturing processes. More particularly, SiC is used as starting material from which, for example, wafer boats or support rings are constructed. Such constructions serve as a holder and positioning means for multiple wafers, which wafers are subjected to several treatment steps during semiconductor fabrication. Such treatment process steps are performed under specific, well controlled conditions as regards to temperature, pressure and vacuum and can be the deposition of several semiconductor material layers on said wafers, for example using chemical vapor deposition techniques (CVD) or other process steps, such as temperature annealing.
It should be noted in this patent application that the term “silicon carbide substrates” includes not only wafer boat holders, but also other constructions or components made from a SIC material, which are used in semiconductor manufacturing processes, for example, in reactor vessels.
As the subsequent treatment process steps of the semiconductor manufacturing processes (such as semiconductor layer deposition) takes place under accurately controlled circumstances as regard as temperature, pressure and vacuum and also require so-called clean room environments needs to fulfill the highest standard as regard to purity and lack of contaminations, also the SiC substrates need to fulfill to the highest standard as regard to dimensions and thermal behavior.
To this end, the several SiC substrate components which form, for example, a wafer boat holder, are subjected to a mechanical machining operation in order to treat the substrate surface. However the surface treatment by means of a mechanical machining operation results in small, nearly invisible microcracks or holes in the surface of the SiC substrates. These microcracks or subsurface damage adversely affects the different subsequent semiconductor manufacturing processes (e.g., the semiconductor layer deposition or high temperature anneal) as all kinds of contaminations may accumulate in said microcracks, which contaminations can be freed from said micro cracks during the semiconductor process, thereby contaminate the semiconductor layer deposition on the wafers. The latter will result in significantly reduced quality or rejection of products.
A further drawback of the presence of subsurface damage on the SiC substrate is the risk of particle generation and emission during the semiconductor manufacturing processes. Due to the changing thermal conditions during the several semiconductor layer depositions, small SiC particles will come loose from the substrate and hence, contaminate the semiconductor manufacturing process.
It is an object of the invention to provide a method and a silicon carbide substrate as mentioned above which obviates the above-identified drawbacks. According to the invention, said method comprising the steps of selective etching the surface of said SiC substrate using a reactive gas mixture, thereby creating a carbon surface layer on said substrate, and removing said carbon surface layer created on said substrate.
Thus, with the method steps according to the invention, SiC substrates can be obtained with a surface structure that complies with the highest standards as regard to dimensions and purity as required in semiconductor manufacturing processes. Especially, SiC substrates treated according to the steps of the invention are highly suitable for use as wafer boats for handling and containing semiconductor wafers on which subsequent treatment process steps of the semiconductor manufacturing processes (such as semiconductor layer deposition or temperature annealing) are performed under accurate, well controlled working conditions (temperature, pressure and vacuum).
As all subsurface damage in the form of microcracks is removed with the removal of the carbon surface layer, a smooth and clean SIC surface is obtained having an extremely high purity, as also all impurities are removed. Furthermore, due to the removal of the subsurface damaged surface, the generation and emission of particles from the SiC surface, which particles may adversely affect the semiconductor manufacturing process, is herewith avoided.
Hence, with a SiC substrate treated with the method according to the invention, a higher degree of purity can be obtained during semiconductor manufacturing processes with a higher level of accuracy and lesser rejection of products.
In a specific embodiment of the method according the invention is the step of removing said carbon surface layer performed by means of an oxidation treatment technique.
In another embodiment of the method according to the invention is the step of removing said carbon surface layer performed by means of a hydrogenation treatment technique. In another embodiment, the step of removing said carbon surface layer is performed by means of a hydrothermical treatment technique.
Moreover, in an advantageous embodiment of the invention, a functional etching technique the reactive gas mixture being used during the step of etching the surface of said SiC substrate is a halogen-containing gas mixture, wherein the halogen-containing gas concentration of said reactive gas mixture can be 100%.
In another embodiment according to the invention, the halogen-containing gas is chlorine (Cl2), for example, in an Argon-environment.
Furthermore, in another advantageous embodiment with an excellent etching performance, the reactive gas mixture also contains hydrogen (H2).
In an example, the flow rate of said reactive gas mixture is 0.5-5 liters per minute, whereas, the working pressure of said reactive gas mixture may lie between 100 mbar and the ambient pressure, and wherein the working temperature of said reactive gas mixture may lie between 1000° C. and 1200° C.
The SiC substrate for use in semiconductor manufacturing processes is, according to the invention, characterized in that said SiC substrate comprising a surface, wherein on said surface a carbon surface layer is formed by means of an etching technique using a reactive gas mixture, which carbon surface layer is subsequently removed from said substrate.
Likewise is in an specific embodiment of the SiC substrate according to the invention, said carbon surface layer removed by means of an oxidation treatment technique. Or said carbon surface layer can be removed by means of a hydrogenation treatment technique.
Likewise said carbon surface layer can be removed by means of a hydrothermical treatment technique.
In a specific embodiment of the SiC substrate according to the invention, said SiC substrate surface is subjected to a reactive gas mixture consisting of a reactive gas mixture containing a halogen-containing gas mixture.
Furthermore, in a more specific embodiment, said halogen-containing gas concentration of said reactive gas mixture is 100%, and more in particular, said halogen-containing gas is chlorine (Cl2) in an Ar-environment. Furthermore, the reactive gas mixture may also contain hydrogen (H2).
Likewise the flow rate of said reactive gas mixture may lie between 0.5-5 liters per minute, whereas said SiC substrate surface may be subjected to a working pressure of said reactive gas mixture between 100 mbar and the ambient pressure, or whereas said SiC substrate surface is subjected to a working temperature of said reactive gas mixture between 1000° C. and 1200° C.